Standard solid-phase immunoassays with monoclonal antibodies involve the formation of a complex between an antibody adsorbed on a solid support (capture antibody), the antigen, and an antibody to another epitope of the antigen conjugated with a detectable label (tracer antibody). Thus, a sandwich is formed: solid support-capture antibody-antigen-tracer antibody. In the sandwich, the intensity of the antibody-conjugated detectable label is proportional to the antigen concentration in the incubation medium. The standard sandwich method is also called double antigen bridging immunoassay because capture and tracer antibodies bind to different epitopes of the antigen. Hoesel, W., et al., in J. Immunol. Methods 294 (2004) 101-110, report an anti-EPO double antigen bridging assay whereby a mixture of immobilized rhEPO coupled to amino groups and to carbohydrate groups was used.
Immunoassays such as the double antigen bridging ELISA are common assay types in the investigation of an immunogenic answer of a patient to an antibody drug (therapeutic or diagnostic antibody). Mire-Sluis, A. R., et al., in J. Immunol. Methods 289 (2004) 1-16, summarize the recommendations for the design and optimization of immunoassays using detection of host antibodies against biotechnology products. According to Mire-Sluis et al. the well-known anti-drug antibody assay formats show considerable disadvantages. Anti-drug antibody assays are mentioned, for example, in WO 2005/045058; and WO 90/006515. Anti-idiotypic antibody assays are mentioned, for example, in U.S. Pat. No. 5,219,730; WO 87/002778; EP 0 139 389; and EP 0 170 302. Wadhwa, M., et al., in J. Immunol. Methods 278 (2003) 1-17, report strategies for the detection, measurement and characterization of unwanted antibodies induced by therapeutic biologicals.
Serological analysis of human anti-human antibodies is described in Ritter, G., Cancer Res. 61 (2001) 6851-6859, and WO 2003/016909. The identification of human anti-human antibodies of IgG class requires an additional step of protein G precipitation prior to the assay.